This invention relates to a combined electrosurgical-cryosurgical instrument for tissue ablation.
Radiofrequency (RF) tissue ablation is a technique for making thermal lesions in tissue. The technique involves inserting a RF probe into tissue and then supplying the tip of the RF probe with RF energy. The tissue around the tip of the probe coagulates due to the heat produced surrounding the tip of the probe. The technique is commonly used to destroy tumors and other diseased tissue. The RF probe can be used superficially, surgically, endoscopically, laparascopically, or interstitially.
A RF lesion results from tissue destruction due to resistive heating that occurs in tissue surrounding the RF probe. Because resistive heating decreases rapidly as the distance from the RF probe increases, and because RF probes cause charring in the affected tissue, the size of lesions that have been obtained using conventional techniques have been limited. Typically, the maximum transverse diameter of RF lesions is about 10-15 mm. Organ L. W., Electrophysiologic Principles of Radiofrequency Lesion Making, Appl. Neurophysiol. 1976, 39:69-70.
Another technique for tissue ablation involves the use of a cryoprobe. Instead of heating tissue to cause it to coagulate, a cryoprobe destroys tissue by freezing it. One cryogenic tissue ablation technique involves inserting a cryoprobe into tissue and then providing a cryogen to the tip of the cryoprobe. As used herein, a cryogen is a substance such as, for example, a gas or a liquid, that provides a cryogenic effect. Typically, a high pressure cryogen gas is directed to the tip of the cryoprobe and then allowed to expand quickly, thereby producing a Joule-Thompson effect at the cryoprobe tip. Common cryogenic tissue ablation techniques involve the use of high pressure (e.g., about 80 psi) liquid nitrogen systems or high pressure (e.g., 2,800 psi) Joule-Thompson argon gas systems. In either method, the tissue surrounding the tip of the cryoprobe is frozen due to the cryogenic effect at the tip of the probe.
Thermal tissue ablation is replacing surgical tissue removal in many applications in the treatment of cancerous and benign conditions. Freezing (cryo-ablation) and heat (radiofrequency ablation) have been used successfully in various organs to destroy abnormal tissue. Radiofrequency ablation and cryo-ablation have different and potentially complimentary advantages. Cryo-ablation""s advantages include the ability to create large lesions that are easily monitored using ultrasound and to have a beneficial immunologic effect. However, cryolesions often produce a toxic response in the patient when the lesions break down. This is because the cryo-ablation process does not denature the patient""s tumor proteins. Radiofrequency lesions, on the other hand, have the advantage of being homeostatic while producing less systemic toxic effects because the ablated tissue is completely denatured. However, radiofrequency lesions usually cannot be made as large as cryolesions and are difficult to monitor using ultrasound.
U.S. Pat. No. 5,951,546 (Lorentzen) describes an electrosurgical instrument for tissue ablation. The instrument has a cooling supply that provides cooling fluid to the instrument during the tissue ablation process. The cooling fluid is used to cool the shaft of the instrument in order to prevent or reduce charring of tissue that is associated with radiofrequency lesion formation. The Lorentzen patent does not describe a combined electrosurgical-cryosurgical tissue ablation instrument. The entire contents of U.S. Pat. No. 5,951,546 are expressly incorporated by reference herein.
U.S. Pat. No. 5,906,612 (Chinn) describes a cryosurgical probe having insulating and heating sheaths. A thermally insulating sheath surrounds the cryosurgical probe. The size and shape of the ice ball produced by the probe can be controlled by varying the length and thickness of the thermally insulating sheath and the length of the distal tip of the probe. Alternatively, the size and shape of the ice ball can be controlled by surrounding the cryosurgical probe with a heated sheath having a heating element and a temperature sensor to detect the temperature to which the sheath is heated. The Chinn patent does not describe a combined electrosurgical-cryosurgical tissue ablation instrument. The entire contents of U.S. Pat. No. 5,906,612 are expressly incorporated by reference herein.
U.S. Pat. No. 4,202,336 (van Gerven) describes cauterizing probes for cryosurgery. The cryosurgical probe described in the van Gerven patent has a heating coil close to the freezing tip which operates through a highly heat conductive portion of the probe wall so as to cauterize previously frozen tissue. The disclosed heating coil does not produce a radiofrequency lesion. The van Gerven patent also describes a probe for cauterization only. That probe has the same heater, temperature sensor and insulating tip as the cryosurgical probe but it is equipped for circulating cooling water rather than cryogenic flow in the cooling space.
U.S. Pat. No. 5,807,395 (Mulier, et al.) describes a method and apparatus for radiofrequency ablation of tissue. In the disclosed method, radiofrequency ablation is accompanied by the infusion of a conductive solution into the tissue being treated so that a virtual electrode is created. The conductive fluid increases the conductivity of the tissue in the area being treated. As a result, the area of tissue being treated is enlarged as compared with non-fluid-assisted radiofrequency tissue ablation.
None of the aforementioned references describes or suggests a tissue ablation instrument that can be used to produce both a cryolesion and a radiofrequency lesion. Such an instrument would be highly desirable because it would permit medical personnel to make both types of lesions in a given area of tissue without having to remove the first tissue ablation instrument and insert a second tissue ablation instrument in the same place. In addition, such an instrument may provide the added benefit of facilitating creation of hybrid lesions which exhibit the advantageous characteristics of both cryolesion and radiofrequency lesions.
Consequently, there is a need in the art for a tissue ablation instrument that may be used to produce both a cryolesion and a radiofrequency lesion.
There is a further need in the art for a tissue ablation instrument that may be used to produce lesions that exhibit the advantageous characteristics of both cryolesions and radiofrequency lesions.
The present invention is directed towards a combined electrosurgical-cryosurgical instrument for tissue ablation comprising a shaft having a proximal end and a distal end, the distal end being electrically and thermally conductive; a radiofrequency insulation sheath surrounding the outer surface of the shaft, defining a radiofrequency-insulated portion of the shaft and a radiofrequency-noninsulated portion of the shaft; a cryo-insulation sheath surrounding a surface of the shaft, defining a cryo-insulated portion of the shaft and a cryo-noninsulated portion of the shaft; a radiofrequency power source connected to the shaft, wherein the power source provides electrical energy to the distal end of the shaft; a cryogen supply tube within the shaft, the cryogen supply tube extending from the proximal end of the shaft to the distal end of the shaft, wherein the cryogen supply tube has an open end portion at the distal end of the shaft; and a cryogen supply source connected to the proximal end of the cryogen supply tube.
In one embodiment, the instrument may be constructed such that the portion of the shaft that produces a radiofrequency lesion overlaps, partially or substantially entirely, with the portion of the shaft that produces a cryolesion. In this embodiment, the radiofrequency insulation sheath surrounds a portion of the outer surface of the shaft. The radiofrequency insulation sheath extends from the proximal end of the shaft to the distal end of the shaft, but leaves a portion of the distal end of the shaft uncovered. A cryo-insulation sheath surrounds a portion of the inner surface of the shaft. The cryo-insulation sheath extends from the proximal end of the shaft to the distal end of the shaft, but leaves a portion of the distal end of the shaft uncovered. Thus, a portion of the distal end of the shaft may be used to create a radiofrequency lesion, a cryolesion, and/or a lesion having characteristics of both a radiofrequency lesion and a cryolesion.
In another embodiment, the instrument may be constructed such that the portion of the shaft that produces a radiofrequency lesion is adjacent to a portion of the shaft that produces a lesion having characteristics of both a radiofrequency lesion and a cryolesion. In this embodiment the cryo-insulation sheath extends from the proximal end of the shaft to the distal end of the shaft, but leaves a portion of the distal end of the shaft uncovered. The radiofrequency insulation sheath surrounds a portion of the outer surface of the shaft. The radiofrequency insulation sheath extends from the proximal end of the shaft to the distal end of the shaft to a position that is proximal to the distal end of the cryo-insulation sheath.
In another embodiment, the instrument may be constructed such that the portion of the shaft that produces a radiofrequency lesion is adjacent to the portion of the shaft that produces a cryolesion. In this embodiment the radiofrequency insulation sheath surrounds a portion of the outer surface of the shaft. The radiofrequency insulation sheath extends from the proximal end of the shaft to the distal end of the shaft, but leaves a portion of the distal end of the shaft uncovered. A discontinuous cryo-insulation sheath surrounds the inner surface of the shaft. A first segment of cryo-insulation sheath extends from the proximal end of the shaft to the distal end of the shaft, but leaves a portion of the distal end of the shaft uncovered. The portion of the distal end of the shaft left cryo-noninsulated by the first segment of cryo-insulation sheath extends from a position proximal to the distal end of the radiofrequency insulation sheath to the distal tip of the shaft. A second segment of cryo-insulation sheath extends from the distal end of the radiofrequency insulation sheath to the distal tip of the shaft. In this embodiment, the instrument may be used to provide a radiofrequency lesion adjacent to a cryolesion. With respect to the instrument shaft, the radiofrequency lesion is provided distal to the cryolesion.
In another embodiment, the placement of the radiofrequency insulation sheath and cryo-insulation sheath may be reversed so that, with respect to the instrument shaft, the radiofrequency lesion is made adjacent to and proximal to the cryolesion. In this embodiment, the cryolesion insulation sheath surrounds the inner surface of the shaft and extends from the proximal end of the shaft to the distal end of the shaft, but leaves a portion of the distal end of the shaft cryo-noninsulated. A discontinuous radiofrequency insulation sheath surrounds the outer surface of the shaft. A first segment of radiofrequency insulation sheath extends from the proximal end of the shaft to the distal end of the shaft, but leaves a portion of the distal end of the shaft radiofrequency-noninsulated. The portion of the distal end of the shaft left radiofrequency-noninsulated by the first segment of radiofrequency insulation sheath extends from a position proximal to the distal end of the cryo-insulation sheath to the distal tip of the shaft. A second segment of radiofrequency insulation sheath extends from the distal end of the cryo-insulation sheath to the distal tip of the shaft. The radiofrequency lesion is thereby provided proximal to the cryolesion.
In all of the previously described embodiments, the cryo-insulation sheath may surround the outer surface of the shaft. The cryo-insulation sheath may lie between the radiofrequency insulation sheath and the outer surface of the shaft. Alternatively, the radiofrequency insulation sheath may lie between the cryo-insulation sheath and the outer surface of the shaft.
In another embodiment, the combined electrosurgical-cryosurgical instrument of the invention may have a single sheath that provides both radiofrequency insulation and cryo-insulation. In this embodiment, the radiofrequency insulation and cryo-insulation sheath surrounds a portion of the outer surface of the shaft. The portion of the shaft used to make a radiofrequency lesion is the same portion of the shaft that is used to make a cryolesion.
This invention also is directed towards a sheath for a tissue ablation instrument having an electrically insulating tubular surface and a radiofrequency power source connected to the electrically insulating tubular surface. The tubular surface has a first opening at a proximal end and a second opening at a distal end. When the sheath is placed over a surgical probe it surrounds the outer surface of the probe, and the radiofrequency power supply source makes electrical contact with the surgical probe. The sheath extends from the proximal end of the probe to the distal end of the probe while leaving a portion of the distal end of the probe radiofrequency-noninsulated. Consequently, the probe may be used to create a radiofrequency lesion in tissue. When the sheath is placed over a cryoprobe, a portion of the distal end of the probe may be used to create a radiofrequency lesion, a cryolesion, and/or a lesion having characteristics of both a radiofrequency lesion and a cryolesion.
It is an object of the present invention to provide a tissue ablation instrument that may be used to produce both a cryolesion and a radiofrequency lesion.
It is another object of the present invention to provide a tissue ablation instrument that may be used to produce lesions that exhibit the advantageous characteristics of both cryolesions and radiofrequency lesions.
Yet another object of the present invention is to provide a radiofrequency insulation sheath equipped with a radiofrequency power supply source, which radiofrequency sheath may be placed over a cryosurgical instrument to provide an instrument which may be used to produce both a cryolesion and a radiofrequency lesion.
These and other objects, features and advantages of the present invention may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments and by reference to the appended drawings and claims.